(GUARDIAN) — A teenage boy underwent “unimaginable physical torture” before being drowned by his sister and her partner because they believed he was a sorcerer who was practising witchcraft, a court heard on Thursday.

Eric Bikubi and Magalie Bamu, both 28, killed 15-year-old Kristy Bamu in their east London flat after violently abusing him for several days, and repeatedly attacked the victim’s two sisters, whom they accused of sorcery, the Old Bailey heard on the opening day of the trial.

Over four days Kristy, who was visiting his sister from France, was tortured with metal bars, wooden sticks, a hammer and a pair of pliers in a “prolonged attack of unspeakable savagery and brutality”, the court was told.

After being denied sleep and food and having being repeatedly attacked, Kristy admitted to being a sorcerer in the hope that the violence would stop. He finally begged to be allowed to die.